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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.high_resolution_timer"></a><a class="link" href="high_resolution_timer.html" title="high_resolution_timer">high_resolution_timer</a>
</h3></div></div></div>
<p>
        <a class="indexterm" name="asio.indexterm.high_resolution_timer"></a> 
Typedef for a timer
        based on the high resolution clock.
      </p>
<pre class="programlisting">typedef basic_waitable_timer&lt; chrono::high_resolution_clock &gt; high_resolution_timer;
</pre>
<h5>
<a name="asio.reference.high_resolution_timer.h0"></a>
        <span><a name="asio.reference.high_resolution_timer.types"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.types">Types</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/clock_type.html" title="basic_waitable_timer::clock_type"><span class="bold"><strong>clock_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The clock type.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/duration.html" title="basic_waitable_timer::duration"><span class="bold"><strong>duration</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The duration type of the clock.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/executor_type.html" title="basic_waitable_timer::executor_type"><span class="bold"><strong>executor_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The type of the executor associated with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/time_point.html" title="basic_waitable_timer::time_point"><span class="bold"><strong>time_point</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The time point type of the clock.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/traits_type.html" title="basic_waitable_timer::traits_type"><span class="bold"><strong>traits_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The wait traits type.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<h5>
<a name="asio.reference.high_resolution_timer.h1"></a>
        <span><a name="asio.reference.high_resolution_timer.member_functions"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.member_functions">Member Functions</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/async_wait.html" title="basic_waitable_timer::async_wait"><span class="bold"><strong>async_wait</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Start an asynchronous wait on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/basic_waitable_timer.html" title="basic_waitable_timer::basic_waitable_timer"><span class="bold"><strong>basic_waitable_timer</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Constructor. <br> <span class="silver"> &#8212;</span><br> Constructor to set a particular expiry
                  time as an absolute time. <br> <span class="silver"> &#8212;</span><br> Constructor to set a particular
                  expiry time relative to now. <br> <span class="silver"> &#8212;</span><br> Move-construct a basic_waitable_timer
                  from another.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/cancel.html" title="basic_waitable_timer::cancel"><span class="bold"><strong>cancel</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Cancel any asynchronous operations that are waiting on the timer.
                  <br> <span class="silver"> &#8212;</span><br> (Deprecated: Use non-error_code overload.) Cancel
                  any asynchronous operations that are waiting on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/cancel_one.html" title="basic_waitable_timer::cancel_one"><span class="bold"><strong>cancel_one</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Cancels one asynchronous operation that is waiting on the timer.
                  <br> <span class="silver"> &#8212;</span><br> (Deprecated: Use non-error_code overload.) Cancels
                  one asynchronous operation that is waiting on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_after.html" title="basic_waitable_timer::expires_after"><span class="bold"><strong>expires_after</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Set the timer's expiry time relative to now.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_at.html" title="basic_waitable_timer::expires_at"><span class="bold"><strong>expires_at</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use expiry().) Get the timer's expiry time as an absolute
                  time. <br> <span class="silver"> &#8212;</span><br> Set the timer's expiry time as an absolute
                  time. <br> <span class="silver"> &#8212;</span><br> (Deprecated: Use non-error_code overload.)
                  Set the timer's expiry time as an absolute time.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_from_now.html" title="basic_waitable_timer::expires_from_now"><span class="bold"><strong>expires_from_now</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use expiry().) Get the timer's expiry time relative
                  to now. <br> <span class="silver"> &#8212;</span><br> (Deprecated: Use expires_after().) Set the
                  timer's expiry time relative to now.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expiry.html" title="basic_waitable_timer::expiry"><span class="bold"><strong>expiry</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Get the timer's expiry time as an absolute time.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/get_executor.html" title="basic_waitable_timer::get_executor"><span class="bold"><strong>get_executor</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Get the executor associated with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/get_io_context.html" title="basic_waitable_timer::get_io_context"><span class="bold"><strong>get_io_context</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use get_executor().) Get the io_context associated
                  with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/get_io_service.html" title="basic_waitable_timer::get_io_service"><span class="bold"><strong>get_io_service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use get_executor().) Get the io_context associated
                  with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/operator_eq_.html" title="basic_waitable_timer::operator="><span class="bold"><strong>operator=</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Move-assign a basic_waitable_timer from another.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/wait.html" title="basic_waitable_timer::wait"><span class="bold"><strong>wait</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Perform a blocking wait on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/_basic_waitable_timer.html" title="basic_waitable_timer::~basic_waitable_timer"><span class="bold"><strong>~basic_waitable_timer</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Destroys the timer.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<p>
        The <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput">basic_waitable_timer</code></a>
        class template provides the ability to perform a blocking or asynchronous
        wait for a timer to expire.
      </p>
<p>
        A waitable timer is always in one of two states: "expired" or "not
        expired". If the <code class="computeroutput">wait()</code> or <code class="computeroutput">async_wait()</code> function
        is called on an expired timer, the wait operation will complete immediately.
      </p>
<p>
        Most applications will use one of the <a class="link" href="steady_timer.html" title="steady_timer"><code class="computeroutput">steady_timer</code></a>,
        <a class="link" href="system_timer.html" title="system_timer"><code class="computeroutput">system_timer</code></a>
        or <a class="link" href="high_resolution_timer.html" title="high_resolution_timer"><code class="computeroutput">high_resolution_timer</code></a>
        typedefs.
      </p>
<h5>
<a name="asio.reference.high_resolution_timer.h2"></a>
        <span><a name="asio.reference.high_resolution_timer.remarks"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.remarks">Remarks</a>
      </h5>
<p>
        This waitable timer functionality is for use with the C++11 standard library's
        <code class="computeroutput">&lt;chrono&gt;</code> facility, or with the Boost.Chrono library.
      </p>
<h5>
<a name="asio.reference.high_resolution_timer.h3"></a>
        <span><a name="asio.reference.high_resolution_timer.thread_safety"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.thread_safety">Thread
        Safety</a>
      </h5>
<p>
        <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
      </p>
<p>
        <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Unsafe.
      </p>
<h5>
<a name="asio.reference.high_resolution_timer.h4"></a>
        <span><a name="asio.reference.high_resolution_timer.examples"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.examples">Examples</a>
      </h5>
<p>
        Performing a blocking wait (C++11):
      </p>
<pre class="programlisting">// Construct a timer without setting an expiry time.
asio::steady_timer timer(io_context);

// Set an expiry time relative to now.
timer.expires_after(std::chrono::seconds(5));

// Wait for the timer to expire.
timer.wait();
</pre>
<p>
        Performing an asynchronous wait (C++11):
      </p>
<pre class="programlisting">void handler(const asio::error_code&amp; error)
{
  if (!error)
  {
    // Timer expired.
  }
}

...

// Construct a timer with an absolute expiry time.
asio::steady_timer timer(io_context,
    std::chrono::steady_clock::now() + std::chrono::seconds(60));

// Start an asynchronous wait.
timer.async_wait(handler);
</pre>
<h5>
<a name="asio.reference.high_resolution_timer.h5"></a>
        <span><a name="asio.reference.high_resolution_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.changing_an_active_waitable_timer_s_expiry_time">Changing
        an active waitable timer's expiry time</a>
      </h5>
<p>
        Changing the expiry time of a timer while there are pending asynchronous
        waits causes those wait operations to be cancelled. To ensure that the action
        associated with the timer is performed only once, use something like this:
        used:
      </p>
<pre class="programlisting">void on_some_event()
{
  if (my_timer.expires_after(seconds(5)) &gt; 0)
  {
    // We managed to cancel the timer. Start new asynchronous wait.
    my_timer.async_wait(on_timeout);
  }
  else
  {
    // Too late, timer has already expired!
  }
}

void on_timeout(const asio::error_code&amp; e)
{
  if (e != asio::error::operation_aborted)
  {
    // Timer was not cancelled, take necessary action.
  }
}
</pre>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            The <code class="computeroutput">asio::basic_waitable_timer::expires_after()</code> function
            cancels any pending asynchronous waits, and returns the number of asynchronous
            waits that were cancelled. If it returns 0 then you were too late and
            the wait handler has already been executed, or will soon be executed.
            If it returns 1 then the wait handler was successfully cancelled.
          </li>
<li class="listitem">
            If a wait handler is cancelled, the <a class="link" href="error_code.html" title="error_code"><code class="computeroutput">error_code</code></a>
            passed to it contains the value <code class="computeroutput">asio::error::operation_aborted</code>.
          </li>
</ul></div>
<p>
        This typedef uses the C++11 <code class="computeroutput">&lt;chrono&gt;</code> standard library
        facility, if available. Otherwise, it may use the Boost.Chrono library. To
        explicitly utilise Boost.Chrono, use the <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput">basic_waitable_timer</code></a>
        template directly:
      </p>
<pre class="programlisting">typedef basic_waitable_timer&lt;boost::chrono::high_resolution_clock&gt; timer;
</pre>
<h5>
<a name="asio.reference.high_resolution_timer.h6"></a>
        <span><a name="asio.reference.high_resolution_timer.requirements"></a></span><a class="link" href="high_resolution_timer.html#asio.reference.high_resolution_timer.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">asio/high_resolution_timer.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
      </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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